Electric incandescent lamp



Oct. 12, 1965 E. H. WILEY 3,211,42

ELEfl'lRIC INCANDESCENT LAMP Filed June 20, 1963 A FIG. 3

CURRENT D INVENTOR. EMMETT H. WILEY TIME BY ATTO R N EY United States Patent 3,211,942 ELECTRIC HNCANDESCENT LAMP Emmett H. Wiley, Willowiclr, Ohio, assignor to General Electric Company, a corporation of New York Filed June 20, N63, Ser. No. 23%189 4 Claims. (Cl. 313315) This invention relates generally to electric incandescent lamps and more particularly to a high efiiciency compact incandescent lamp for photographic purposes.

The high efiiciency electric incandescent lamp disclosed and claimed in US. Patent 2,883,571-Fridrich et al, assigned to the ass-ignee of the present invention, presented a novel and new source tor the photographic industry because of its high lumen efiiciency and high lamp maintenance. In adapting this lamp for photographic purposes, it was necessary to compact the lighted filament length so that the light output of the lamp could be more easily controlled by conventional reflectors and lens system, such reflectors and lens system being primarily designed to ntilize -a compact source of light. In shortening the source length, the lead tip spacing was correspondingly reduced. The lead tip spacing determines the length of gap for the are that develops at lamp failure. Since there are temperature limitations on the envelope glass itself, the wall of the envelope must be a greater distance away from the lighted filament so as to avoid overheating from the increased wattage concentration. Thus, the compacting of the source for photographic purposes results in an arc gap which is less than /3 as long as the prior lamps \and having a diameter approximately /3 greater than the prior lamps operating on the same source voltage. These photographic lamps have more than 60 volts per inch of lead tip spacing as compared with less than 60 volts per inch of lead tip spacing in general purpose lighting lamps of this type. In commercial practice of photographic lamps of this type, the lamps may have 200 volts per inch of lead tip spacing or more. With the above limitation as to the geometry of the lamp, the are that occurs at lamp failure has a very low impedance even with are suppressing fill gas such as nitroge This low impedance permits very high currents to flow at these voltages unless a means of limiting this current and stopping the arc is provided For example, at end of lamp lite, the lamp in effect becomes a discharge lamp which will carry arc therethrough which becomes, on ionization of the gas, a low-resistant, high-current path through the lamp. Because the ionized arc is of low resistance, the lamp may draw current of about 80 amperes for a sufficient length of time I o create a dangerous hazard since the lamp seals and also the household wiring into which the lamp is normally connected are not designed for carrying such a high current.

It is an object of this invention to provide a lamp of the above-mentioned type which is provided with a fuse leg or end as an integral part of the filament to obviate the above-mentioned hazard.

Further objects and advantages of this invention will appear from the following detailed description of the preferred embodiment thereof and from the drawing wherein:

FIG. 1 is a side view of a lamp provided with a fuse end or leg in accordance with the invention;

FIG. 2 is an enlarged section view of the ends of the lamp, hetter illustrating the preferred embodiment of the invention; and

FIG. 3 is a series of current Waveform-s illustrating the results obtained by use of the invention.

Referring to FIG. 1 of the drawing, the lamp comprises an elongated tubular envelope 1 of vitreous material such as glass or quartz, having a flat pinch seal 2 at each end thereof which may be pressed to an Lshaped cross-section giving strength and rigidity.

A filament 3, which is a coiled-coil of tungsten wire, having a short source length and hence, a short lead tip spacing, extends axially of the envelope. In the art the terms source length and lead tip spacing are interchange-able and refer to the distance between the ends of the inca-ndescible portion of the filament. However, it Will be noted from the following description that some distinction must be made with reference to the instant lamp and therefore, as related to this case, the term source lengt refers to the distance between the ends of the coiled-coil portion of the filament which produces most of the light emitted from the lamp. The source length may also be defined as the distance within the lamp wherein at least 97% of the voltage drop in the lamp appears. As is well known, the higher efiiciencies for tungsten filaments are achieved by operating the filament at higher temperature levels and for photographic purposes it is desirable to operate the lamp rat the higher efiiciency. Therefore, with the lamp operating at these high efficiencies and with a short source length, the voltage per inch of source length is greater than 60 volts per inch. To keep the wall of the tubular envelope .1 spaced away from the coiled-coil filament 3 of the compacted lamp, it is necessary that the diameter of the envelope be at least /5 the dimension of the source length,

A lead-in conductor 5 having an extremely thin foliated portion 5a and a spud 6 extends through and is hermetically sealed in one of the pinch seals 2. A helically single coiled end 4- of the filament 3 is inserted over the spud 6 to support one end of the coiled-coil filament 3. The other end of the coiled-coil filament has a straight uncoiled leg or fuse end 7 as an integral part of the filament and is composed of the originally straight tungsten wire from which the filament has been coiled. The straight leg 7 is secured directly to la foliated portion 8 of the lead-in conductor which is sealed Within the other pinch seal 2.

Lamps of this type normally operate on approximately 56 amperes of current through the filament during normal operation. However, since the cold resistance of the tungsten wire is lower than its operating resistance, the lamp upon turn-on receives a current inrush which may amount to approximately amperes. Therefore, the leads 5 and 9 and foliated portions 5:: and 8 are designed to carry approximately 40 amperes current to prevent destruction of the seals during current inrush. Higher currents through the current inleads for short periods of time usually result in violent failure of the seals 2. It is not economical to design the current lead-in conductors for higher amperage since, in normal operation of the lamp, it is not necessary and under extraordinary extended periods at high current loadings the household wiring or other wiring to which the lamp may be connected is not constructed for these high currents. Therefore, the fuse end or leg 7 is provided integrally within the lamp envelope to protect the lamp seals and the external circuitry from damage from high currents under extraordinary conditions which develop at lamp failure in the lamp.

The envelope preferably contains an inert gas filling and a reactive atmosphere of iodine as disclosed and claimed in Patent 2,883,571Fridrich et al. The inert gas is preferably nitrogen because of the well known are suppressing ability of this gas. A filling or argon, for example, results in arcing within the lamp even prior to the end of lamp life.

A lamp to which the invention is particularly directed has a 650 watt coiled-coil filament operating on a 120 volt source. The source length is approximately .75 inch so the voltage per inch of lead tip spacing is approximately 160. To compensate for source compaction the lamp is a T-4 which hasan inside diameter of approximately .4 inch which gives a diameter source length ratio greater than /2.

The current characteristic of a lamp of the above type constructed in accordance with the prior art, i.e., with spu-ds do at both ends of the lamp, is shown by wave form A of FIG. 3. The lamp operating current 31 is about 6 amperes. A filament failure causes an arc to form within the lamp which arc, being of low resistance, permits are current 32 of about 80 amperes to flow. The lamp seals in this case did not fail so that the increased pressure within the lamp eventually quenched the arc. This is to be compared with wave form B wherein the lamp operating current 33 and arc current 34 are again shown. In this case the lamp seals failed at 35 and the lamp envelope exploded. From this, the necessity for providing appropriate fusing for lamps having more than 60 volts per inch lead tip spacing is readily apparent.

Wave form C shows the operation of another lamp constructed in accordance with the prior practice having a 6 ampere fuse in the circuit for protection at lamp failure. The lamp current 36 being 6 amperes no lower rating fuse may be used but still the arc current 37 rose to approximately 80 amperes before the fuse failed at 38 to open the circuit. It should be noted that the fuse failed at approximately the same time that the unfused lamp of wave form B exploded, so it is apparent that with ordinary fusing of the lamp, the possibility exists of violent lamp failure prior to open circuiting by the fuse. The use of a fuse which is rated at nearly the same current level as the operating level of the lamp is further not desirable since it may fail merely in turn-on or ordinary operation, but the use of higher rated fusing is barred by the hazardous possibilities.

Wave form D shows the current characteristics of a lamp constructed with a fuse end or leg 7 in accordance with the invention. The lamp operating current 39 is again about 6 amperes and the arc current 40 rose above this level to about 40 amperes before the circuit was opened at 41. It should be noted that the arc lasted for only approximately /2 of the time of arc duration in wave form C. While the exact mechanism providing this improvement is not fully known, it is believed that operation of the are directly on the fuse leg 7 causes a rapid destruction thereof back to the point where the metal enters the pinch seal 2. At this point the constricted area of the envelope serves to quench the arc.

The use of a straightened end portion of the tungsten filament otters the distinct advantage of being easily manufactured during the ordinary filament coiling operation. While lower melting point metals may be used to take advantage of the quenching action of the envelope walls, the use of metals besides molybdenum or platinum may in terfere with tungsten-iodine regenerative cycle. The use of the same size tungsten wire of the filament for the fuse eliminates the problem of matching the fuse rating with the lamp current since it inherently has the same characteristics.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A compact high efiiciency electric lamp comprising a substantially tubular light-transmitting envelope; a coiled-coil incandescible filament of tungsten wire extending longitudinally within said envelope having a short source length and a voltage of more than 60 volts per inch of said source length; the envelope having a diameter greater than /5 of the source length; a filling in said envelope of nitrogen gas and a quantity of iodine sufficient to promote a regenerative getter action; pinch seals constricting the interior of the envelope and hermetically sealing the ends of the envelope; lead-in conductors enclosed in and extending externally of said pinch seals, at least one of said lead-in conductors terminating within its associated pinch seal, and means connecting said lead-in conductors to respective ends of said filament including an uncoiled straight wire longitudinally extending leg portion of the tungsten filament at least at one end thereof and extending directly into the one of said pinch seals containing the lead-in conductor terminating therewithin and connected to said conductor within the pinch seal whereby said leg portion serves as a fuse.

2.. A compact high efficiency electric lamp comprising a substantially tubular light-transmitting envelope; at coiled-coil incandescible filament of tungsten wire extending longitudinally within said envelope having a short source length and a voltage of more than 60 volts per inch of said source length; a filling in said envelope of nitrogen gas and a quantity of iodine sufficient to promote a regenerative getter action; pinch seals constricting the interior of the envelope and hermetically sealing the ends of the envelope; lead-in conductors enclosed in and extending externally of said pinch seals, at least one of said leadin conductors terminating within its associated pinch seal; and means connecting said lead-in conductors to respective ends of said filament including an uncoiled straight wire longitudinally extending leg portion of the tungsten filament at least at one end thereof and extending directly into the one of said pinch seals containing the lead-in conductor terminating therewithin and connected to said conductor within the pinch seal, whereby said leg portion serves as a fuse.

3. A compact high efficiency electric lamp comprising a substantially tubular light-transmitting envelope; a coiled-coil incandescible filament of tungsten wire extending longitudinally within said envelope having a short source length and a voltage of more than 60 volts per inch of said source length; a filling in said envelope of an inert gas and a quantity of iodine sufficient to promote a regenerative getter action; pinch seals constricting the interior of the envelope and hermetically sealing the ends of the envelope; lead-in conductors enclosed in and extending externally of said pinch seals, at least one of said lead-in conductors terminating within its associated pinch seal, and means connecting said lead-in conductors to respective ends of said filament including an uncoiled straight wire longitudinally extending leg portion of the tungsten filament extending directly into the one of said pinch seals containing the lead-in conductor terminating therewithin and conected to said coductor within the pinch seal whereby said leg portion serves as a fuse.

4. A compact high efficiency electric lamp comprising a substantially tubular light-transmitting envelope; a coiled-coil incandescible filament of tungsten wire extending longitudinally within said envelope having a short source length and a voltage of more than 60 volts per inch of said source length; the envelope having a diameter greater than /5 of the source length; a filling in said envelope of nitrogen gas and a quantity of iodine sufficient to promote a regenerative getter action; pinch seals constricting the interior of the envelope and hermetically sealing the ends of the envelope; lead-in conductors enclosed in and extending externally of said pinch seals, a first one of said lead-in conductors terminating within its associated pinch seal, and means connecting said lead-in conductors to respective ends of said filament including a spud constituting part of the second lead-in conductor and extending from the associated pinch seal into the interior of the envelope and inserted in a coiled end of the filament and an uncoiled straight wire longitudinally extending leg portion of the tungsten filament extending directly into the one of said pinch seals containing the first one of said lead-in conductors and connected thereto Within the associated pinch seal whereby said leg portion serves as a fuse.

References Cited by the Examiner UNITED STATES PATENTS Bartlett 2001l5.5 Linder 200115.5 Swanson 313222 X Anderson 200-131 X Duval 313-222 X DAVID J. GALVIN, Primary Examiner. JAMES D. KALLAM, Examiner. 

1. A COMPACT HIGH EFFICIENCY ELECTRIC LAMP COMPRISING A SUBSTANTIALLY TUBULAR LIGHT-TRANSMITTING ENVELOPE; A COILED-COIL INCANDESCIBLE FILAMENT OF TUNGSTEN WIRE EXTENDING LONGITUDINALLY WITHIN SAID ENVELOPE HAVING A SHORT SOURCE LENGTH AND A VOLTAGE OF MORE THAN 60 VOLTS PER INCH OF SAID SOURCE LENGTH; THE ENVELOPE HAVING A DIAMETER GREATER THAN 1/5 OF THE SOURCE LENTGH; A FILLING IN SAID ENDVELOPE FOR NITROGEN GAS AND A QUANTITY OF IODINE SUFFICIENT TO PROMOTE A REGENERATIVE GETTER ACTION; PINCH SEALS CONSTRICTING THE INTERIOR OF THE ENVELOPE AND HERMETICALLY SEALING THE ENDS OF THE ENVELOPE; LEAD-IN CONDUCTORS ENCLOSED IN AND EXTENDING EXTERNALLY OF SAID PINCH SEALS, AT LEAST ONE OF SAID LEAD-IN CONDUCTORS TERMINATING WITHIN ITS ASSOCI- 